Many papers have been published lately on chemical bath deposition of CdS (CBD-CdS) thin films and related materials due to the promising results obtained using CBD-CdS for the fabrication of thin-film solar cells. In spite of this little of the research proposes a realistic chemical mechanism for the deposition process based on the determination pf kinetic parameters. In this paper we present an exhaustive study of the CBD-CdS kinetic from which we propose a new chemical mechanism which agrees with the kinetic parameters determined supported by heterogeneous catalysis concepts. Simultaneously, the dependence of the deposited filth structure on the kinetic variables is studied and the results obtained corroborate the proposed mechanism. These studies have allowed us to stablish a standard set of conditions for the fabrication of homogeneous and continuous very thin CdS films.